(CNN) – The United States should not take action in Syria, because it would appear to be siding with an opposition force that has extremist elements, Sen. Rand Paul said Monday in the debut of CNN's new "Crossfire."

"We've seen priests beheaded by the Islamic rebels...We've also seen an Islamic rebel eating the heart of a soldier. So it's not like there's no atrocity on the other side, and al Qaeda is on the other side," he said. "I can't conceive of how we would go in and be allies with al Qaeda."

On the left: Stephanie Cutter. On the right: Newt Gingrich. In the Crossfire, Senator Rand Paul, who opposes a military strike on Syria and Senate Foreign Relations Chairman Robert Menendez, who supports a limited strike.

Tune to CNN at 6:30pm ET for the debate and jump into the conversation on our live blog using your desktop or mobile device.

Sen. Robert Menendez and Sen. Rand Paul join hosts Newt Gingrich and Stephanie Cutter in the Crossfire to debate a congressional authorization for a Syria strike.

We want you to weigh in on the debate: If you were in Congress, would you vote to authorize a strike on Syria? Vote below or tweet your response using #CrossfireReturns. You can also vote by commenting on our Facebook post.